DNA methylation has been implicated in neuronal functions and mental disorders but these studies were limited to a few candidate genes. Understanding the role of DNA methylation in neuronal development and disease requires knowledge of the distribution of methylated cytosines in the entire genome and in specific neuronal prototypes whose function can be directly linked to normal and pathological behavior. Here we propose i) to employ genome-wide representational DNA methylation analyses to characterize the distribution of mCpGs in glutamatergic and GABAergic projection neurons in the hippocampus and striatum, respectively, as well as in neuronal precursors and mouse embryonic stem (ES) cells to follow methylation during development. The neurons selected for this study are involved in important functions including spatial learning/memory (dorsal hippocampus), emotional behavior (ventral hippocampus), locomotor activity (dorsal striatum) and drug abuse and social behavior (ventral striatum/nucleus accumbens). Since all of these behaviors are influenced by the maternal environment, we also propose ii) to determine the effect of adverse pre/early postnatal maternal environment on neuronal DNA methylation in animals sensitive and resilient to these effects. We have previously established two animal models which are based on maternal mutations leading to permanent behavioral abnormalities in genetically normal offspring, including abnormal fear, stress responsiveness, overall activity and social interaction. We expect that our studies will identify DNA methylation signatures specific a) for neuronal prototypes, b) for their developmental stages (neuronal precursor, young and mature neurons), c) for their dorso-ventral position and d) for adverse maternal effects. The high resolution methylation assay used in this proposal will help to determine not only the overall pattern of methylation but also to generate assemblies of genes marked by methylation. These groups of genes form functional networks and pathways that are essential to understand the role of DNA methylation in neuronal development and psychiatric disease.